Fashion on street, not so hot? (7)
I believe the answer is:
average
'not so hot?' is the definition.
('not so hot' can mean mediocre or average)
'fashion on street' is the wordplay.
'fashion' becomes 'rage' (something all the rage is fashionable).
'on' means one lot of letters go next to another.
'street' becomes 'ave' (short for avenue).
'rage' put after 'ave' is 'AVERAGE'.
(Other definitions for average that I've seen before include "Moderate" , "Arithmetic mean" , "building society customer loses capital over time" , "It may be mean" , "Mean - everyday" .)